lassiter



June 20, 1939. A. D LASSlTER 7 Re; 21,121

TALKING MOTION PICTURE APPARATUS Original Filed April 5, 1952 2Sheets-Sheet l 14.6! Patna-5179a! IN VEN TOR.

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June 20, 1939. A. o LASSITER TALKING MOTION PICTURE APPARATUS OriginalFiled April 5, 1932 2 Sheets-Sheet 2 INVENTOR. afivwgw 9. J

5 ATTORM Reiasued June 20, 1939 "UNITED STATES 21,121 TALKING MOTIONPICTURE APPARATUS Alwyn D. Lassiter, Philadelphia, Pa., assignor, by

mesne assignments, to Western Electric Com- D y, York Incorporated, acorporation of New Original No. 2,104,428, dated January 4, 1938, Se-

rial No. 603,390, April 5, 1932.

Application for reissue April 5, 1939, Serial No. 266,231

22 Claims.

My invention relates broadly to talking motion picture systems and moreparticularly to a circuit arrangement for and construction of soundreproducing system for operation in conjunction with the projection ofmotion pictures.

One of the objects of my invention is to provide a circuit arrangementfor talking motion picture systems wherein the entire equipmentincluding the amplification system, sound repro ducing device, exciterlamps and photoelectric cells of a talking motion picture system, may beoperated from the usual alternating current source available in theprojection booth of a theatre.

Another object of my invention is to provide a construction of portablesound reproducing apparatus for operation under control of the soundrecord on a film wherein the alternating current lighting circuit powermay be utilized for energizing all parts of the sound reproducing systemincluding the exciter lamp, the photo electric cell, the severalcircuits of the electron tubes employed in the amplification system andthe field circuit of the sound reproducer.

Still another object of my invention is to provide a control circuit fora sound reproducing system by which the amplification circuit of thesound reproducing system may be controlled from either of twophotoelectric cell systems installed on. adjacent projectors in a motionpicture booth with means for gradually fading the sound record of onefilm at the end of a reel on one projector into the sound record at thebeginning of the film on the other projector.

A further object of my invention is to provide an arrangement ofautomatic switching device operative at the time that connections areestablished with the photoelectric cell circuit of one projector withthe amplification system of the sound reproducer for energizing theexciter lamp in the sound head of that projector while tie-energizingthe exciter lamp in the sound head of the adjacent projector.

A still further object of my invention is to provide an amplificationcircuit for operating sound reproducer. the input of the amplificationcircuit being controllable from the sound head of either of two adjacentprojectors with means for fading in the effect of the sound head of oneprojector while fading out the effect of the sound head of the adjacentprojector at the time of changeover between reels on the projectors.

Another object of my invention is to provide means for selectivelycontrolling the volume of sound in a sound reproducing system controlledfrom a sound film record for insuring uniform reproduction of sound fromeither of two projectors which are operated for successive runs fordisplaying successive reels of a motion picture with soundaccompaniment.

Still another object of my invention is to provide a circuit arrangementfor an amplification system in a talking motion picture apparatusincluding successive electron tube stages successively coupledconductively and inductively in an arrangement which insures theaccurate reproduction of sound over a broad audio frequency range withminimum distortion.

Another object of my invention is to provide a construction of portablemounting means for the amplification and sound reproduction apparatus ofmy invention for increasing the portability of the equipment.

Other and further objects of my invention re side in the soundreproducing apparatus and circuit arrangement therefor as set forth morefully in the specification hereinafter following in which:

Figure 1 diagrammatically illustrates the circuit arrangement of thesound reproducing system of my invention; Fig. 2 is a perspective viewof the amplification apparatus of my invention with the cover thereofremoved to show the mounting of the parts therein; Fig. 3 is aperspective view of the portable carrying case and sound reproducerforming part of my invention; and Fig. 4 illustrates the covering memberof the portable carrying case and showing the manner of mounting thesound reproducer therein.

This application is a continuation in part of my application Serial No.579,972 filed December 9, 1931, entitled Audio frequency amplificationsystem, now Patent No. 2,072,114, granted March 2, 1937.

Referring to the drawings in detail, I have designated the terminals ofthe amplifier system and power supply circuits for the exciter lamps ofthe projectors at I, 2, 3, 4, 5, and 6. The control tube of theamplifier system is indicated at 24. The tube 24 is a five electrodetube including a cathode 24o, a heater element 24b, a control grid 240,a shield grid 24d and an anode 24c. The output circuit of the controltube 24 is coupled through a resistance and capacity coupling system'l-l9 to the input circuit of the power amplifier tube 21 which is inturn coupled through resistance-capacity coupling I l5|2-82 to the inputcircuit of power amplifier tube 28. The output circuit of poweramplifier tube 28 is coupled through audio frequency transformer 83 tothe input circuit of power amplifier tube 50. The sound reproducer B6 isshown as including an electromagnetic field 81 and a movable armaturewinding 88 connected with the conical diaphragm 80. The output of thepower amplifier tube 50 connects through transformer 9 to armaturewinding 88 of the sound reproducer 86. A condenser 85 is employedconnected between the grounded side of the secondary of transformer 9and the core of the transformer for eliminating undesired noises in thesound reproducing circuit. The field winding 81 of the sound reproducer86 is energized from rectified alternating current supplied from thepower supply system which includes the rectifier tubes 8|. The entireapparatus is energized from the alternating current power supply sourceusualy available in a motion picture booth or in a residence where theapparatus of my invention may be readily operated. The alternatingcurrent power supply is connected with terminals 95 which lead to theprimary circuits of transformers 29 and 96. Transformer 29 includesprimary winding 30 and secondary windings 3| and 32. Transformer 95includes primary Winding 91 and secondary windings B8, 99, N10, and NH.The secondary windings 3| and 32 connect to points 3311 and 33brespectively on the dry type rectifier 33. The output terminals of thedry type rectifier 33 are represented at 330 connected through filtercircuit 34 to the output leads 35, which leads extend to the heaterfilaments 24b and 21b of the tubes 24 and 21 respectively. Properregulation of the current supp-lied to the heater filaments 24b and 21bis obtained by means of resistance 2'! connected across power supplycircuit 35. The distribution circuit to the heated filaments 24b and211) has been illustrated at 36. One side of the circuit is extendedthrough conductor 3'! to the contacts 38 of the shiftable switch 43. Theswitch 43 has a yoke extension lfi thereon which is disposed in the pathof the angularly shiftable arm 41a movable aboutpivot 41. The arm 41aengages the yoke 45 of switch arm 43 and serves to shift switch arm 43either to the right or the left against the action of spring H6. Spring6 operating upon switch 43 enables switch 43 to be mounted. inthelimiting position to which the switch is moved. Switch 43 carriescontacts 45 which serve to shunt fixed contacts 440: and 441) with thecontacts 38. Contact 44a connects with terminal 3 of the input system'tothe amplifier. Contact 44b connects to terminal 60f the input system tothe amplifier. A connection extends from terminal 3 to the incandescentfilament of exciter lamp 4| in the sound head of the first motionpicture pro- J'ector. The other side of the incandescent filament ofexciter lamp 4| connects to terminal I which is connected to ground 13.

It will be observed that the opposite side of the power supply'circuitleading'from filter 34 is grounded at 39 so that in this way a returnpath to the power source is established from exciter lamp 4|. Thecontact 44b which connects to terminal 6 of'the amplifier electricallyconnects with one side of the exciter lamp 42 of the second projector.The opposite side of incandescent lamp 42 is connected to terminal 2which is connected to ground '13. The control tube 24 has the controlgrid 24c thereof connected to a midtap 5| on potentiometer 4B. The end52 of potentiometer 48 connects through condenser 54 to terminal 4 ofthe amplifier system to the cathode of light sensitive cell 62 in thesecond sound head projector, the anode of which is connected to groundthrough terminal 2. The opposite end 53 of potentiometer 48 connectsthrough condenser 55 with terminalii of the amplification system whichconnects to the cathode of light sensitive cell 6| in the first soundhead projector. The anode of light sensitive cell 6| connectsto groundthrough terminal I. The circuit is thus completed to the potentiometer48 from light sensitive cells 6| and 62. In order to render either ofthe sound heads effective upon thecontrol tube 24, the movable contact48 which extends from the rotary pivot 41 is moved to selected positionsalong potentiometer 48. The contact 49 is connected to terminal I of theamplifying system and is electrically connected to ground 13. Thus apredetermined resistance extending between terminal .52 and contact 49on potentiometer 48 may be included in shunt with light sensitive cell62 when the cell is electrically connected in the input circuit oilcontrol tube 24. Similary a portion of resistance extends betweencontact 45 and terminal 48 may be included in shunt with light sensitivecell SI for effectively controlling the operation of the light sensitivecell with 'respect to the control tube 24. By moving contactor 49 overpotentiometer 48 various degrees of control from the light sensitivecells'6l and 62 are obtained so that the control by one light sensitivecell may be graduallyfaded out while the control of the otherphotoelectric cell is being faded in. This enables the amplificationsystem to be utilized in a motion picture projection booth where theamplification apparatus is mounted to cooperatively function with twoprojectors.

The sound reproduction system for the first projector includes exciterlamp 4|, optical system 68, sound film 54 light sensitive cell chamber63 and light sensitive cell 6|. The sound head on the second projectorincludes incandescent lamp 42, optical system 69, sound film 65, lightsensitive cell chamber 66 and light sensitive cell 62.

In order to control the volume of the reproduced sound, I provide a setof resistors ll which are electrically connected in the arrangementshown for controlling the potential supplied to the input circuit ofcontrol tube 24 in series with light sensitive cell 6| or 62. Theresistors l1 electrically connect with impedances |8-92 and'|493 in theseparate circuits shown. Impedances |493 connect through conductor 90with resistors 14 and 15 which respectively control the current to thelight sensitive cell circuits including light sensitive cells 6| and 62and regulate the current to the input of control tube '24. Resistors l8and 92 connect with the filter circuit 9| in the output of the full-waverectifier constituted by rectifier'tubes 8|. Power is supplied to thetubes 8| from windings I00 and I 0| on transformer 96. Winding I00supplies cathode heating current while winding ||l| supplied anodepotential. Secondary winding 99 of transformer 96 supplies cathodeheating current for power amplifier tube 56. The mid-tap connection I03which; extends from winding '99 passes to ground 94 through. resistor 22and serves to impose a C-bias on tube 50. The secondary winding 98supplies heating current for the heater'filament 28b of power amplifiertube 28. A potentiometer is shunted across winding 38 and the mid-tap 12thereof electrically connected with the mid-tap on secondary winding |6|and the grounded side of the filter circuit 9| which connects with therectifier tubes 8|. Resistors 22 and I9 having the midconnection thereofgrounded at 34 provide means for controlling the potential to the lightsensitive circuits and to the input of the control tube 24. Resistanceelements 23 and 26 are arranged in circuit with impedance l9 andelectrically con nected with the field winding 81 of sound reproducer 86for regulating the potential supplied to the field winding of the soundreproducer. The proper biasing potential is supplied to the input ofpower amplifier tube 21 through resistors 8-9 and 2I-20 arranged asshown. Connection is made to ground at 80 from taps I, 9, and 20 asshown. Proper potential is supplied to the output circuit of tube 21through resistance I0, The required operating potential is supplied forthe output circuit of tube 28 through resistors I5 and I6 connected asshown. The windings of transformer 03 are connected to ground at 84 forobtaining the required operating potential on the grid of tube 50 asshown.

The required operating potential for anode 24c of control tube 24 isobtained by means of the connection through the resistors indicated atI, 0, and 9. The required potential for biasing the grid 210 of tube 21is obtained through resistance II connected to ground I0. The inputcircuit of control tube 24 is completed from cathode 24a throughresistance I6 to ground Ill. The current from the dry type rectifier andassociated filter 34 is indicated by meter 34a. The voltage supplied tothe primary winding 91 of power transformer 96 is indicated by voltmeter91a.

In Fig. 1 I have illustrated the relative arrangement of the amplifyingapparatus as being disposed between projector #1 and projector #2.

Figs. 2, 3, and 4 illustrate the manner in which the parts of theamplifying apparatus and sound reproducer are mounted. Fig. 2 shows abase I04 having protective casings and shields I05 and I06 thereon whichhouse parts of the cou pling circuits, power transformers, the dry typerectifier and the elements of the filter system.

The base I04 has latch members II at each end thereof adapted tocooperate with hook members I08 carried by the cover portion I09 of thecarrying case in which the sound reproducer 06 is mounted. The carryingcase has handle members IIO attached thereto to facilitatetransportation of the equipment. The cone diaphragm of the soundreproducer BB is shown at 89 arranged at one wall of the casing whichhouses the sound reproducer. A detachable plug III is connected with aflexible conductor II2 which may be coiled and stowed within the casingI00 by means of securing strip H3. The supporting base I 04 providesmounting means for electron tubes 24, 21, 28, 50, and BI as shown. Thesupporting base carries transformers 83 and 9 as shown. The socketsindicated at L and R on the base I04 contain the terminals I, 3, and andthe terminals 2, 4, and 6 for connection through plugs with the soundheads on the opposite motion picture projectors in accordance with thewiring arrangement illustrated in Fig. 1. The control tube 41b issecured to the rotatable shaft 41 illustrated in Fig. 1 and is shiftablein the direction L or R for the purpose of fading in and fading out therespective sound heads. I have shown an electrostatic shield 24bpositioned over the control tube 24. The casings I05 and I06 providemounting means for control switches and also serve to support meters 97aand 34a. As heretofore noted, meter 91a. reads the voltage across theprimary of power transformer 96 while meter 34a shows the current to theheater filaments 34b and 21b and to the exciter lamps 4! and 42. Thecover I09 is provided with peripheral latches III thereon which serve assupports for the base I 04 which carries the amplifying apparatus.

The compact arrangement of the amplification system of my invention hasproven highly satisfactory in operation. The cooperative effectsobtained by the conjoint operation of the conductive and inductivecouplings in the different stages of the amplifier is such as to permitthe supplying of the circuits of the exciter lamps directly over thecircuit from the filament heaters of the first stages of amplificationin the. amplification system and the utilization of direct current atthe exciter lamps Where steady illumination is essential. The conductiveand inductive coupling system also insures accurate reproduction in thelow projection of frequencies encountered in talking motion picturesysterns as well as throughout the musical frequency range. Thearrangement of the circuits is such that undesired oscillations areprevented in the audio frequency range obtained. The light sensitivecells may be supplied from the same source of power supply whichfurnishes potential to the plate circuits of the amplifier tubes therebyrendering the apparatus extremely compact. Movement of control tube 41?)on base I04 enables the sound record on one projector which is nearingthe end of a reel to be faded out while the sound record on the firstreel of the adjacent projector is being faded in.

I have found the apparatus of my invention efiicient in its operationand capable of inexpensive manufacture and although I have described myinvention in one of its preferred embodiments I desire that it beunderstood that modifications may be made and that no limitations areintended other than are imposed by the scope of the appended claims,

What I claim as new and desire to secure by Letters Patent of the UnitedStates is as follows:

1. Talking motion picture apparatus comprising an amplification system,a sound reproducer connected with said amplification system, a controltube connected with the input of said amplification system, a pair oflight sensitive cells subjected to variations of light under control ofindependent film records, a potentiometer connected between the inputcircuit of said control tube and said light sensitive cells, and meansfor variably controlling the effective value of said potentiometer withrespect to each of said light sensitive cells and for fading the efiectof the sound record to which one of said light sensitive cells issubjected in, while fading the sound record to which the other of saidlight sensitive cells is subjected out in said sound reproducer, and asource of rectified and filtered alternating current operativelyconnected to the aforesaid amplification system, the field of the soundreproducer, and the light sensitive cells.

2. Talking motion picture apparatus comprising an amplifier system, asound reproducer connected with the output of said amplifier system, acontrol tube connected with the input of said amplifier system, a pairof independent sound heads each including a light sensitive cellcontrolled by a sound film record, means electrically connecting saidlight sensitive cells with the input circuit of said control tube, anda, variable impedance device for selectively controlling the effect ofsaid light sensitive cells upon said contro-l tube in a reciprocalmanner, and a source of rectified and filtered alternating currentoperatively connected to the aforesaid amplification system, the fieldof the sound reproducer, and the light sensitive cells.

3. Talking motion picture apparatus comprising an amplification system,a sound reproducer controlled by said amplification system, a controltube connected with the input circuit of said amplification system,separate sound heads for motion picture projectors each including alight sensitive cell forming part of the talking motion pictureapparatus, an impedance device coupling the light sensitive cell in eachof said sound heads with the input of said control tube, and means forvarying the effect of said impedance device on said light sensitivecells in a reciprocal manner for fading in the effect of one of saidsound heads while fading out the effect of the other of said sound headswith respect to the operation of said sound reproducer, and a source ofrectified and filtered alternating current operatively connected to theaforesaid amplification system, the field of the sound reproducer, andthe light sensitive cells.

4. Talking motion picture apparatus comprising an amplification system,a source of power for energizing the circuits of said amplificationsystem, a sound reproducer connected with the output of saidamplification system, a pair of sound heads each including an eXciterlamp, a light sensitive cell and a sound film record for varying theeffect of said exciter lamp on said sound film record, means forcoupling said light sensitive cells to the input circuit of said controltube, means for variably controlling the effect of one of said lightsensitive cells with respect to the effect of the other of said lightsensitive cells, and means controlled by the operation of the lastmentioned means for controlling the operation of the exciter lamps ofsaid sound heads from the source of power which energizes saidamplification system.

5. Talking motion picture apparatus comprising an amplification system,a source of power for energizing the circuits of said amplificationsystem, a sound reproducer connected with the output of saidamplification system, a control tube connected with the input of saidamplification system, a pair of sound heads each including an exciterlamp, a light sensitive cell and a film record for variably controllingthe effect of the exciter lamp upon said light sensitive cell, animpedance element, means for selectively connecting said light sensitivecells to the input circuit of said control tube through said impedanceelement, means for selectively controlling the value of said impedancewith respect to each of said light sensitive cells, and a switchactuated by said last mentioned means for completing connections betweensaid power source and each of said exciter lamps when the sound headwith which the said exciter lamp is associated is rendered effective forcontrolling said sound reproducer.

6. Talking motion picture apparatus comprising a multi-stage amplifiereach including an electron tube having a filament, a control grid and ananode electrode, circuits interconnecting said electrodes, analternating current power supply circuit, means for deriving rectifiedcurrent from said power supply circuit, circuits for energizing thefilaments of selected electron tube from alternating current derivedfrom said power supply circuit, circuits for energizing the filaments ofothers of said electron tubes from rectified current derived from saidpower supply cir cuit, a sound reproducer connected to the outputcircuit of the last amplification stage, light sensitive cells connectedto the input circuit of the first amplification stage, exciter lampsindividual to each of said light sensitive cells and means forenergizing said exciter lamps from the filament circuits of saidelectron tubes which are energized from rectified current.

7. In a talking motion picture apparatus, an alternating current powersupply circuit, an electron tube amplification system having a soundreproducer connected with the output circuit thereof and a lightsensitive cell connected with the input circuit thereof, an exciter lampadjacent said light sensitive cell and means for energizing said exciterlamp and certain of the electron tubes in said amplification system fromrectified current derived from said alternating current power circuit.

8. Talking motion picture apparatus comprising a multi-stage electrontube amplification system, a sound reproducer connected with the outputof said amplification system, an alternating current power supplycircuit for energizing the power circuits of said electron tubeamplification system, a light sensitive cell connected in the inputcircuit of said amplification system, an exciter lamp focused upon saidlight sensitive cell for operation in conjunction with a sound film forVariably controlling said light sensitive cell and rectification meansconnected with the alternating current power supply circuit forenergizing portions of the electron tubes in certain of theamplification stages of said amplification system and energizing saidexciter lamp for effecting the operation of said sound reproducer.

9. Talking motion picture apparatus comprising an alternating currentpower supply circuit, a multi-stage amplification system comprising aplurality of electron tubes each having filament, a control grid and aplate, a sound reproducer connected to the output circuit of saidamplification system, a light sensitive cell connected with the inputcircuit of said amplification system, means for deriving rectifiedalternating current and raw alternating current from said alternatingcurrent power supply circuit, means for energizing the filaments ofcertain of said electron tubes from raw alternating current, a circuitfor energizing the filaments of others of said electron tubes fromrectified alternating current, an exciter lamp disposed adjacent saidlight sensitive cell and circuit connections for energizing said exciterlamp from rectified alternating current derived from said last mentionedcircuit.

10. In a talking motion picture system, an amplification circuit, asound reproducer connected with the output of said amplificationcircuit, a control tube connected with the input of said amplificationcircuit, a pair of resistance elements connected in the input of saidcontrol tube, a light sensitive cell connected across a portion of eachof said resistance elements, an exciter lamp individual to each of saidlight sensitive cells, and means for controlling the energization ofeach of said light sensitivecells and simultaneously controlling theeffectiveness of said light sensitive cells upon the input of saidcontrol tube.

11. In a talking motion picture apparatus, an amplification system, asound reproducer connected with the output of said amplification system,a control tube connected with the input of said amplification system, apair of separate sound heads each including an exciter lamp, an opticalsystem, a sound film and a light sensitive cell, a power supply source,a two-position switch, and means for mechanically actuating saidtwoposition switch for electrically connecting said power source witheither of said exciter lamps and simultaneously connecting the lightsensitive cell in the sound head of the said exciter lampwith the inputcircuit of said control tube.

12. In a talking motion picture apparatus, an amplification system, asound reproducer connected with the output of said amplification system,a control tube connected with the input of said amplification system, apair of sound heads each including an exciter lamp, an optical system, asound record and a light sensitive cell, a potentiometer having themidpoint thereof connected with the control grid of said control tube,one end of said potentiometer being connected with one terminal of oneof said light sensitive cells and the other end of said potentiometerbeing connected with a terminal of the other of said light sensitivecells, a variable tap on said potentiometer for selectively controllingthe efiect of either of said light sensitive cells upon said controltube, an actuating arm movable simultaneously with the adjustment ofsaid variable tap and a. two position switch controlled by saidactuating arm for selectively connecting either of said exciter lampswith a power source.

13. In a sound-on-film projecting apparatus, an alternating currentpower supply, an electron tube amplification system having a soundreproducer connected with the output circuit thereof and a lightsensitive cell connected with the input circuit thereof, an exciter lampfor said light sensitive cell, and means for applying polarizingpotential to the light sensitive cell comprising rectifier and filterdevices connected to the alternating current power supply.

14. In a sound-on-film projecting apparatus, an alternating currentpower supply, an electron tube amplification system having a soundreproducer connected with the output circuit thereof and a lightsensitive cell connected with the input circuit thereof, an exciter lampfor said light sensitive cell, and means for energizing said exciterlamp, the filaments of the electron tubes of the amplifier, and thefield coil of the loud speaker, said means comprising rectifier andfilter devices connected to the alternating current power supply.

15. In a sound-on-film projecting apparatus, an alternating currentpower supply, an electron tube amplification system having a soundreproducer connected with the output circuit thereof and a lightsensitive cell connected with the input circuit thereof, an exciter lampfor said light sensitive cell, and means for applying potential to thelight sensitive cell and the plate circuits of the amplifier comprisingrectifier and filter devices connected to the alternating current powersupply.

16. In a sound-on-film projecting apparatus, an alternating currentpower supply, an electron tube amplification system having a soundreproducer connected with the output circuit thereof and a lightsensitive cell connected with the input circuit thereof, an exciter lampfor said light sensitive cell, and means for energizing the exciterlamp, the light sensitive cell, the amplifier and the sound reproducerfield devices and circuits comprising two sets of rectifier and filterdevices, one set for energizing and applying potential to some of theforegoing and the other set for energizing and applying potential to theremainder of same.

17. A system for reproducing sound embodying, in combination, a sourceof illumination, a photoelectric cell, a photographic record of sound,means to cause said record to travel between said source and said cell,means for reproducing said sound controlled .from said cell, a source ofalternating current, a rectifier and a filter in the supply circuit forsaid source of illumination and operating from said source ofalternating current, said filter being arranged to reduce variations inthe current supply to said source of illumination to such an extent thatthe effect of said variations is less than the efiect of variations inthe remainder of the system.

18. In a sound reproducing system, in combination, a source ofillumination, a photoelectric cell, a film having a photographic recordof sound, means to cause said film to travel between said source andsaid cell, means controlled from said cell for reproducing said sound, asource of alternating current, a supply circuit for said source ofillumination comprising a rectifier and a filter operated from saidsource of alternating current and arranged to reduce the variations insaid alternating current to such value that the noise caused by saidvariations produces no perceptible increase in the noise produced byother irregularities in said system.

19. A method of reproducing sound embodying in combination a source ofillumination, a photoelectric cell, a photographic record of sound,means to cause said record to travel between said source and said cell,means for reproducing said sound controlled from said cell, a source ofalternating voltage, a rectifier and a filter operated from said sourceof alternating voltage to supply a polarizing potential to said cell andarranged to reduce the variations in said potential to such value thatthe noise produced by said variations causes no perceptible increase inthe noise produced by other irregularities in said system.

20. In a sound reproducing system, in combination, a photoelectric cell,a lamp exciting said cell, a photographic record of sound, means tocause said record to travel between said source and said cell, athermionic amplifier controlled from said cell, a source of alternatingvoltage, a rectifier and a filter operated from said source ofalternating voltage to supply a potential to said cell and the platecircuits of said amplifier and arranged to reduce the variations in saidpotential to such value that the noise produced by said variations isnot materially greater than the noise produced by irregularities in saidsound record.

21. In a sound reproducing system, in combination, a photoelectric cell,a lamp exciting said cell, a film having a photographic record of sound,means to cause said film to travel between said lamp and said cell, athermionic amplifier controlled from said cell, a source of alternatingcurrent, a supply circuit for said lamp and the filaments of saidamplifier operated from said source comprising a rectifier and a filterand arranged to reduce the variations in said alternating current tosuch value that the noise caused by said variations produces noperceptible increase in the noise produced by other irregularities insaid system.

22. In combination, an output circuit, a plurality of sound headstherefor, means for traversing consecutive sound record sequences insaid sound heads respectively, an energizing circuit for said soundheads, and means comprising a single potentiometer device connectedbetween said energizing circuit and said sound heads for shifting andfading reproduction in said output circuit from one of said sound headsto another thereof.

ALWYN D. LASSITER.

